1. Field of the Invention
The present invention relates to a wavelength division multiplexing transmission technology for transmitting and receiving a plurality of light waves having different wavelengths over a single optical transmission line. More particularly, this invention is concerned with a wavelength- division multiplexing transmitter receiver having a redundant configuration, an optical transmission system, and a redundant system switching method.
2. Description of the Related Art
Technologies for effectively utilizing a wide frequency band of approximately 20 THz permitted by an optical fiber serving as an optical transmission line have been studied in years. In recent years, development of a technology for handling the wavelength of light including development of optical devices or the like has made progress, an increase in processing speed of an electronic circuit has come to a standstill, and an optical amplifier repeater has made its debut. For these reasons, there is some prospect of realizing a high-speed and large-capacity economic repeater transmission line through combination of a technology of wavelength division multiplexing (WDM) transmission, in which a plurality of light waves having different wavelengths are multiplexed and transmitted over one optical fiber, and a technology of optical amplification repeating transmission, in which the light waves to be multiplexed in wavelength are amplified simultaneously.
Various kinds of apparatuses designed for optical communication are expected to offer high reliability. In particular, apparatuses connected over a trunk are requested to guarantee higher reliability. In a WDM transmission approach, since a large amount of information can be transmitted by performing multiplexing relative to a plurality of wavelengths, it has a significant meaning whether or not high-reliability hardware can be realized.
For a known optical transmitter receiver for transferring a light wave having a single wavelength which has been adopted before the WDM transmission approach is established, a configuration in which, for example, an auxiliary system having the same configuration as a current system is included so that if the current system fails, it can be switched to the auxiliary system has been adopted as a redundant configuration for keeping line reliability high. Like the known redundant configuration, a WDM transmitter receiver may presumably include current systems and auxiliary systems, and thus guarantee high reliability. This redundant configuration includes current systems and auxiliary systems associated with wavelengths of light waves to be multiplexed.
According to the above redundant configuration, if for example, part of current systems for processing a light wave with a certain wavelength fails, the current system is switched to an auxiliary system. At this time, the other parts of the current systems for processing light waves with the other wavelengths (current systems that do not fail) are also switched to auxiliary systems. This poses a problem that use efficiency is poor and a transmitter receiver costs high.